1. Field of the Invention
This invention relates to a braking apparatus for work machines and to a method of actuating that braking apparatus.
2. Description of Related Art
Braking apparatus are known in vehicles and in mobile work machines. They are frequently hydraulic control/regulation systems, which can be controlled by the operator of the work machine. It is also known in connection with electronic control/regulation components to connect hydraulic braking apparatus with corresponding control/regulation circuits and thus to extend the functionality of the braking apparatus in comparison with an only manual braking apparatus.
This is known, for example, from so-called anti-lock braking systems, which are used in the most varied vehicles and which also allow automatic access to the brake cylinders in addition to a manual access of the operator to the brake cylinders. In the case of the anti-lock braking system, this automatic intervention takes place for the purpose of stabilizing the handling or braking behavior of the vehicle.
The invention starts from prior art in which an electronic control/regulation system likewise acts on hydraulic brake cylinders, which can also be controlled manually or by a foot pedal. It is in this respect, however, not a question of the stabilization of the braking behavior or of the handling of a work machine, but rather of the control/regulation of the braking behavior of the work machine.
It is known to couple a processing unit with a hydraulic braking system of the work machine to monitor a parked state of the work machine in which the work machine is not moved and the brakes stop the wheels of the work machine from rolling away in an unwanted manner, for example by starting to roll on a slope. This processing unit can, for example, monitor the movement behavior of the work machine. In this respect, the processing unit can determine whether the work machine is in a parked state in which the desired speed is zero. If it is next determined by the processing unit that the actual speed differs from the desired speed, the processing unit can thus initiate an automatic braking procedure in response to the difference.
In a similar situation, the processing unit can determine that the work machine is in a work state in which the desired speed of the vehicle is likewise zero. Analogous to the aforesaid case, the processing unit can effect automatic braking on determining a difference between the desired speed and the actual speed.
The known solutions, however, have some serious disadvantages. In the known apparatus, a single-circuit structure of the braking function is present as a rule. This means that a processing unit switches a valve in the automatic braking procedure. If there is now a disturbance in the apparatus such as a leak in the hydraulic drive or a valve defect, a malfunction of the automatic braking procedure cannot be prevented as a rule. There is no possibility of ensuring a correct function of the braking function despite a leak or a valve defect.
It is also not possible to react correctively to a defective brake actuation in the known braking apparatus, as the brakes could be actuated or released in an unwanted manner.
A malfunction of the braking apparatus can also be caused by a cable break. This is the case when a current is applied to the valve and the brakes release as a consequence of an interruption of the power supply. An unwanted actuation of the brakes can furthermore also be caused via a positive connection to the valves.